Differential Ca2+ Signaling Induced by Activation of the Epidermal Growth Factor and Nerve Growth Factor Receptors

Stimulation by epidermal growth factor (EGF) of NIH3T3 cells overexpressing the EGF receptor (EGFR) results in a release of Ca2+ from internal stores. Ca2+ release is followed by an influx of extracellular calcium which can be recorded by the influx of the calcium surrogate Mn2+. Both Ca2+ release and Mn2+/Ca2+ influx are inhibited by expression of the dominant negative Asn17-Ras mutant and abrogated by microinjected neutralizing anti-Ras antibody Y13-259, whereas microinjection of the anti-Ras antibody Y13-238 which does not interact with the effector binding domain of Ras is without any effect on the EGF-induced Ca2+ transient. Neither Asn17-Ha-Ras nor the Y13-259 antibody interferes with the thapsigargin-induced Mn2+/Ca2+ influx. The nerve growth factor receptor (Trk)-mediated Ca2+ transient was found to be unaffected by the dominant negative Ras mutant or microinjected neutralizing anti-Ras antibodies. Substitution of the phospholipase Cγ1 (PLCγ1) binding site of the EGFR by the PLCγ binding domain of Trk renders the EGFR-induced Ca2+ influx insensitive to the expression of Asn17-Ha-Ras, whereas the Ca2+ signal induced by Trk carrying the PLC binding site of EGFR is Ras-dependent and abrogated by the dominant negative Ras mutant. It is concluded that the Ca2+ transient induced by the activated EGFR, not, however, the Ca2+ transient elicited by the activated NGFR/Trk, is a Ras-mediated phenomenon and that the role of Ras in regulating EGFR-induced Ca2+ influx depends on the structure of the PLCγ binding domain.